Up-and-down motion is a type of motion that involves alternating between two positions, usually up and down. The term can be used to describe a variety of motions, such as nodding one's head or riding a SEESAW. In the context of a crossword puzzle, the solutions for up-and-down motion are NOD (3 letters) and SEESAW (6 letters). NOD is a verb that describes the action of moving one's head up and down in agreement or acknowledgement. SEESAW is a noun that refers to a play structure consisting of a plank balanced on a fulcrum, which allows people to sit on either end and move up and down.